In fastening and excavating technology, manually operable drilling tools are known, which have a driving mechanism for imparting rotary motion to a drilling tool and are equipped with a striking mechanism for producing pulse-like impacts. The axial impacts support the excavating action of the drilling tool, especially when drilling in brittle, failing material, such as concrete, rock, brick masonry and the like. For working on very hard and compact materials, such as concrete and rock, manually operable drilling tools, equipped with an electro-pneumatic striking mechanism, prove to be very appropriate, such handheld or manually operable drilling equipment has long been known and is sold, for example, by the Assignee. The electro-pneumatic striking mechanism of such drilling equipment is designed for producing axial impacts with a high individual impact energy of, for example, about 2 J to about 8 J at a relatively low impact frequency of, for example, about 45 Hz to about 80 Hz. Because of the high energy of the individual axial impacts, manually operable drilling tools are not as suitable for working hollow brick masonry.
Aside from the manually operable drilling tools with an electro-pneumatic striking mechanism, other drilling tools are also known, which have a mechanical striking mechanism. These include the ratchet drills, known primarily for home owner use and the manually operable drills with a spring U-bolt striking mechanism or a spring-cam stroking mechanism employed in semi-professional and professional use. The striking mechanisms of these known handheld drilling tools produce axial impacts with a relatively low single impact energy of, for example, about 0.03 J to about 0.3 J with a relatively high impact frequency, which amounts to about 700 Hz., for example. Because of the low energy of the individual impacts, it is possible to work with impact support on hollow brick masonry with such manually operable drilling tools without destroying the hollow bricks. For working on hard materials, such as concrete or rock, such drilling tools with a mechanical striking mechanism find less use. Because of the low energy of the individual axial impacts, the user of the drilling tool must press relatively strongly against the material and the achievable drilling progress generally is too little for the professional user.
For working different materials, such as concrete and hollow brick masonry, two or more axial impact-supported manually operable drilling tools are required, the axial impacts of which have the single impact energy and impact frequency, suitable for the respective material, in order to work it with sufficient drilling progress, without at the same time damaging it. In general, buildings are not constructed of a continuously homogenous building material. For example, buildings have concrete load-bearing parts and the sections between these parts frequently consist of brick masonry, especially hollow brick masonry. The tool operator, who is to produce boreholes, openings or the like in these different materials in the past always had to use at least two handheld drilling tools with different stroking mechanisms having different impact energies. Since he cannot be expected to carry along two or more manually operable drilling tools at all times, the procurement of the tool, suitable for the respective material, leads to undesirable delays.